[TowerTalk] How high is enough

[Jim Thomson]

Date: Tue, 30 Jul 2013 21:46:28 -0500
From: "Jim in Waco wb5oxq" <wb5oxq_1 at grandecom.net>
To: <TowerTalk at contesting.com>
Subject: [TowerTalk] How high is enough

When choosing a height for a beam is 1/4 wave above ground at the lowest frequency enough?  1/2 wave?  I see Force 12 rating the gain on their beams at 74'1".
Why that height?  At 20 meters is 100' a lot better than say 60'?  I am talking about relatively flat terrain.  I see Stepp-ir makes a beam that even has a 80 meter dipole in it.  Would that workmuch better on 80 than a wire dipole at an equal height?  I have never had enough land to put upmore than 50' bit nest year I might have over an acre and be able to go much higher.  I just wonder how high when you spend more to go higher than it is worth?  If I had the room for a wire dipole to run any direction, what would be the best choice from central Texas considering being in the center of the country east/west wise?  I want to get the best bang for my buck!  wb5oxq

##  F12 uses 74 feet  simply cuz they used a 72 foot tall crank up tower + short mast.   Like others have noted use the info in the ARRL ant book to draw some  conclusions. 
Here in the pacific northwest, higher is better, end of story...at least for dx..and on any band.    My problem with the arrl info is its averaged out over the entire 11 year cycle. 
Typ, when we are in the lower part of the cycle, the  angles are lower, and vice – versa.     You also have to factor in what bands you use.  Throw  40m into the mix, and you
will soon see that  100 feet  eats  50 feet  hands down.  In the pacific north west,  180 feet on 40 m blows away 90 feet  every time  for dx. 

Now add 80m into the equation.  120 feet is barely a half wave up.   And yes, a 80m rotary dipole will easily outperform a  80m fixed wire dipole.   Either 80m ant has a 12-14 db
F-S  ratio....at least on DX signals.....and  4-8 db on local stuff.    With a single, fixed wire dipole,  you can easily lose 4-14 db  just from the dipole being oriented wrong. 
Some folks will use  2 x 80m dipoles...at right angles.... like a T, not an X...to get around this problem.    That works, provides you have 4 x supports. 

Your typ inverted vee on 80m   will radiate just as well off the sides as the ends, and is omni directional  at typ 50-100 foot apex heights.   The shortened  80m rotary dipole 
at 70-100 heights  is a big step above the inverted vee   with its apex at the same 70-100 feet. 

You may also be involved with 50, 144,  220, 440 mhz bands..... line of sight stuff.   Here again, higher is better.   Factoring all of this in,  IF you have a choice, and only one tower
to be installed,  opt for the higher one.   You can also do more stuff  with a taller tower,  like install a lower tribander, on a side mount for high angle signals...and then point
the low and high ants  in different directions too.   Some will opt to just rotate the entire tower..in which case everything points in the same direction.  Some will use tic-ring or
side mounted rotors.   Some will opt for a tall mast  above the top of the tower, to handle more ants.   Some will opt for a 2nd or 3rd tower.   The sky is the limit. 

Of course folks only have so much room, and so much $$.    Do you do most of the operating during the day...or at night ?   A  40m yagi can be used night or day..and
for the entire 11 year cycle.   A 17-15-12-10 m ant is  typ a daytime  operation..and towards the top of the cycle.   If you work day shift...and are busy on weekends,
with family and yard work etc,   17-10m might be a waste  vs a  40m yagi.    It’s a lot of trade offs to consider.  I operate at night, so a 40m yagi + 80m rotary dipole
is my choice.  If you intend on  using 160m, and want to shunt feed the tower,  or hang a qtr wave sloper from the top, or an inverted vee, or use an inverted L , the
taller tower  will be the ticket. 

Later...... Jim   VE7RF